Drawn shell beverage containers, whether fabricated from aluminum or steel, customarily are reduced in diameter proximal to the open end of the container prior to rolling the lid or top onto the container. This reduction in diameter near the top or open end of the container is done primarily to achieve a material saving and consequent cost saving in the lid or top. However, this reduction in diameter near the open end is also effective to reduce the outside diameter of the lid bead to a diameter that is equal to or less than the unnecked portion of the container; and so this reduction in bead diameter facilitates both automatic handling in production and automatic vending.
Machines for performing the necking operation are customarily of the type having a dozen or so working stations and a like number of die sets that are longitudinally disposed with respect to the rotating axis of the drum, and that are circumferentially spaced around the periphery of the drum. Each container is hopper fed to a loading station on the drum, is received into one of the die sets, receives the necking operation while rotating with the drum, and is discharged from the drum prior to the drum completing one revolution of the drum.
Injection of a container into a given working station, forcing of the container into the necking die, coordinated movement of the knockout punch, and forcing of the container out of the necking die by the knockout punch are all controlled by stationary cams that are located at opposite ends of the drum. A machine of this general type is shown and described by Eickenhorst in U.S. Pat. No. 3,635,069.
Forcing of the container out of engagement with the necking die is customarily a mechanical function that is achieved by a shoulder on the knockout punch; and compressed air is customarily used to strip the container off of the knockout punch.
Wright, in U.S. Pat. No. 3,771,344, shows and describes a pneumatic stripping device in which a poppet valve, that is located in the bottom of the punch portion of the die set and that includes an opening stem, is opened by the bottom of the container as the bottom of the container is domed inwardly and actuates the stem inwardly, and is closed by air pressure as the container is pneumatically stripped from the punch and the stem is no longer actuated inwardly with respect to the punch.
Eickenhorst, in the aforementioned patent, shows and describes the use of compressed air to eject a container from a punch portion of a die set after completion of a forming operation wherein the bottom of a container is domed inwardly. The compressed air is valved to each successive working station by a commutating valve that includes an arcuately disposed and angularly positioned slot in the base of a fixed disk.
The valving of the air, in a machine such as taught by Eickenhorst, must be timed so that air is provided within the container not only for stripping the container from the knockout punch but also both for propelling the container backward against a stop plate and for stabilizing the container against the back plate. Thus, the air cannot be shut off early to allow the air pressure in the container to be reduced before the container leaves the punch and the compressed air is exhausted to the atmosphere; and so there is an air blast noise problem which is associated with air stripping which cannot be solved by adjusting the timing of the valving of the air in Eickenhorst's machine. In contrast, the poppet valve arrangement of Wright may provide somewhat of a lower noise level than that of Eickenhorst, although neither inventor mentions noise levels, but Wright's device inherently shuts off the air too soon to adequately stabilize the container against the back plate subsequent to stripping.
The present invention is not concerned with timing of the compressed air as is the above prior art; but, instead provides an expansion chamber in the punch for reduction of air blast noise that is associated with the pneumatic stripping operation.
While compressed air stripping is quite advantageous, as opposed to mechanical stripping, for stripping of delicate thin shell vessels, such as beverage containers, from mandrels and punches, and is extensively used, the noise levels that are associated with air stripping are excessively high and usually exceed present day government noise regulations. Thus, the present invention provides a needed advancement to the prior art, not only to improve operator comfort and to reduce operator fatigue, but also to meet governmental noise regulations.